Experiment 210 was the 210th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to reduce enemy weapons and technology to their primitive state, thus rendering them useless, but could also reduce people and animals to a primitive or prehistoric state. 210 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.
All of the experiment pods were released and scattered across the island of Kauai, with 210's pod landing in a palm tree by a beach.
When a vacationing couple used the palm tree to catapult themselves into a nearby lake, 210's pod fell out of the tree and was accidentally splashed, activating the experiment. 210 then used his tongue to transform the couple's clothes into medieval clothes, their cell phone into a 1930's candlestick telephone, and their car into a 1920's station wagon.
210 later attacked a zoo, reducing some of the animal species to their prehistoric state, including an elephant, tiger, and squirrel.
When Stitch found the answer, he muzzled 210 and took the latter back onto the yacht. There, Stitch released 210, who then turned the yacht into an Ice Age canoe. Stitch then wrapped 210's tongue around Lilo, Jumba, Pleakley, and Nani's junior high friends and spanked his bottom three times, returning the victims to their modern state.
Later, 210, christened Retro, was found a one true place at a wildlife preserve turning modern animals into dinosaurs and prehistoric animals for a Mesozoic zoo.
In "Woops", Retro was oddly seen as one of the captive experiments in Hämsterviel's prison cell, suggesting Gantu caught Retro, but this was an error. Retro was then sent back to Gantu after Experiment 600 caused mischief and nearly blew Hämsterviel's cover to the prison guards.
The first 624 experiments, including Retro, were rounded up by Leroy and taken to a stadium to be destroyed. However, Lilo, Stitch, Jumba, Pleakley, Reuben, and Gantu arrived before the experiments could be destroyed.
Retro participated in the following battle between the experiments and the Leroy clones, but it is unknown what he did. Although he was seen chasing after some of the Leroys, it is uncertain if his powers had any effect on them.
The Leroys soon gained the upper hand in the battle, but were defeated when Lilo, Stitch, Reuben, and several other experiments performed the song "Aloha ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.
Retro made an appearance in a later episode of the Stitch! anime along with Shrink, Squeak, Clip, and Nosox. It is shown that when Retro's powers are used on Stitch, he reverts to his original programming. This is because that was Stitch's earliest state after his creation. He also appeared in the special Stitch and the Planet of Sand.
- In "Woops", Retro erroneously appeared with Gantu's other captive experiments, but he was captured by Lilo and Stitch.
- Retro's pod color is blue.
- Retro is one of the few experiments to not appear in the group photo at the end of Leroy & Stitch.
- In the Stitch! anime, Stitch reverted to his original programming while under Retro's powers, as this was Stitch's earliest state after his creation. Strangely, however, Yuna was able to turn Stitch back to normal by simply reaching out to him and reminding him of his promise, as opposed to reversing the effects the usual way.